The conveying system described in document EP 1559663, dated 2004, explicitly relates to the transport of bottle preforms. This system aims at organizing the flow of the preforms from a random stream into an ordered stream, in order to feed them to a star wheel receiving unit which loads a station where these preforms are heated before they are blown and converted into bottles by an appropriate machine.
Filling the star wheel requires the accumulation of preforms upstream from this wheel, and this accumulation of preforms causes friction between the conveyor members and the preforms which are in single file and touching each other between said conveyor members.
In this document EP 1559663, which is closely related to the object of the invention, the conveyor members are described as consisting of belts in the form of cords having a cylindrical cross-section, made of a material such as natural or synthetic rubber; they may also consist of a metal chain with a covering.
It is also specified in this document EP 1559663 that the friction coefficient is proportioned so that the preforms are advanced by the friction force which can exist, because of adhesion, between said preforms and the conveyor members, said preforms sliding about in the accumulation area until the accumulation pressure required to engage the preforms in the star wheel receiving unit is reached.
One of the means described in that document for adjusting the friction coefficient consists of using a covering which is temporarily applied to the neck of the preforms.
The problem lies in the preforms, which vary in their adhesion to the conveyor members. This adhesion is related to numerous parameters such as the type of material constituting the preforms, or the temperature and the level of humidity where the preforms are being processed. The same is true to a lesser extent for the conveyor members.
The variability of preform adhesion to the conveyor members causes a change in the contact relationship and in the coefficient of friction between the preforms and said conveyor members in the accumulation area, influencing the pressure at which the preforms engage with the receiving unit.
As soon as there is pressure between the preforms and friction between these preforms and the conveyor members, the contact relationship evolves; an increase in temperature in the area of friction is indeed observed and the materials present deteriorate at an ever-increasing rate.
Also, in the preform accumulation area where said preforms and said conveyor members are in sliding contact, the friction between the preforms and the conveyor members, in particular, may lead to damage of the preforms and/or conveyor members caused by abrasion. Such a phenomenon can impact the shaping of the preforms during the blowing operation if they have been damaged, and/or reduce the service life of the conveyor members.
Lastly, the sliding contact between the preforms and the conveyor members in the accumulation area may, depending on the type of conveyor members used, generate significant noise.
A continual increase in production rates, now exceeding 50,000 bottles processed per hour, and the friction/adhesion between the preforms and the conveyor members, are a source of numerous problems in current installations.
The friction coefficient between the preforms and the conveyor members is influenced by the material of the preforms, which affects the adhesion, and by the covering and structure of the surface of the conveyor members.
It is becoming more and more difficult to manage the consequences of friction phenomena due to variations in the adhesion of the preforms to the conveyor members.